Conventionally, an inkjet mechanism for carrying out recording by impacting ink drops on a recording medium is known. This inkjet mechanism includes: a head layer formed by sequentially stacking a first electrode layer, a piezoelectric layer, a second electrode layer and an oscillation layer; an ink chamber partition formed on the oscillation layer of the head layer; and a nozzle plate formed on the ink chamber partition and provided with a nozzle. A space, defined by the head layer, the ink chamber partition and the nozzle plate, forms an ink chamber in which ink is contained. Further, in the inkjet mechanism, upon application of voltage between the first and second electrode layers, the piezoelectric effect of the piezoelectric layer causes the deformation of the head layer and the ink contained in the ink chamber is pressurized, thus discharging the ink from the nozzle.
Actually, the height of the ink chamber in a thickness direction thereof affects the discharge: speed of ink and/or response speed. Therefore, if high definition printing is carried out using an inkjet head that is formed by arranging a large number of inkjet mechanisms, it is preferable that variations in the heights of the respective ink chambers are slight. Furthermore, an ink chamber with an extremely great height causes a reduction in the discharge speed of ink, and is thus not suitable for the inkjet mechanism.
Now, conventional inkjet head fabricating methods are broadly divided into two kinds of methods, i.e., a method for forming an ink chamber by processing a substrate (see FIG. 4) and a method for forming an ink chamber by using a member other than a substrate instead of processing the substrate (see FIG. 5).
In the former method, as shown in FIG. 4A, first, an oscillation layer 101, a first electrode layer 102, a piezoelectric layer 103, and a second electrode layer 104 are stacked in this order over one surface of a substrate 100, thereby forming a head layer 105. Next, as shown in FIG. 4B, a part of the substrate 100 corresponding to an ink chamber 106 is etched away from a surface of the substrate 100 opposite to the head layer 105, thereby forming an ink chamber partition 107. Finally, a nozzle plate 109 provided with an ink discharge opening 108 is bonded onto the ink chamber partition 107 using an adhesive 110 (see Japanese Unexamined Patent Publication No. 10-286960). In this method, the thickness of the substrate 100 is the height of the ink chamber 106 as it is.
Actually, if a plurality of inkjet heads are fabricated on a substrate in order to mass-produce the inkjet heads by employing the former method, it is necessary to use a thin substrate having a large area. However, such a thin substrate having a large area can be very easily broken, and thus the yield is decreased. Therefore, in order to prevent the breakage of a substrate, the following method is proposed: a thick substrate is prepared, a head layer is formed on the substrate, the substrate is polished and thinned, and then an ink chamber is formed. However, since a piezoelectric layer is generally deposited at a high temperature, the substrate is warped at room temperature due to a thermal expansion coefficient difference and/or an internal stress of the piezoelectric layer. Thus, it is difficult to polish the substrate so as to uniformize the thickness thereof. Accordingly, in this method, the heights of ink chambers differ between the simultaneously fabricated inkjet heads, and as a result, there occurs the problem that the printing characteristics differ between the inkjet heads. Because of the above reasons, the former method is not suitable for the mass production of inkjet heads.
On the other hand, in the latter method, as shown in FIG. 5A, first, a first electrode layer 201, a piezoelectric layer 202, a second electrode layer 203, and an oscillation layer 204 are stacked in this order over one surface of a substrate 200, thereby forming a head layer 205. Next, an ink chamber partition 206 and a nozzle plate 208 provided with an ink discharge opening 207 are sequentially bonded onto the oscillation layer 204 of the head layer 205 via adhesives 209, 210. Finally, as shown in FIG. 5B, the substrate 200 is removed by chemical etching. This chemical etching includes wet etching and/or dry etching. According to this method, since the heights of ink chambers can be equalized irrespective of the thickness and/or area of the substrate 200, it is possible to simultaneously fabricate a plurality of inkjet heads in which variations in the heights of the ink chambers are slight. Therefore, in mass-producing the inkjet heads, it is preferable to fabricate them by the latter method.
-Problems that the Invention is to Solve-
However, in the latter method, since the substrate is increased in thickness in order to prevent the breakage of the substrate, a long period of time is required to etch away the substrate. Accordingly, the production efficiency of inkjet heads is reduced.
Further, since a period of time required for the removal of the substrate is long, the electrode layers, adhesives, piezoelectric layer, oscillation layer, ink chamber partition and nozzle plate are degraded during the removal, thus causing variations in ink discharge performance between the simultaneously fabricated inkjet heads.
Furthermore, in the case where dry etching is performed in removing the substrate, if there is contamination of a surface of the substrate subjected to dry etching, the contaminated portion is not dry etched, and as a result, the yield of the inkjet heads might be reduced.
The present invention has been made in view of the above points, and its object is to provide a technique for enabling the simultaneous mass production of inkjet heads in which variations in ink discharge performance are slight, in a method for fabricating an inkjet head including a plurality of piezoelectric elements, each having a first electrode layer, a piezoelectric layer, a second electrode layer and an oscillation layer, for pressurizing ink contained in a plurality of ink chambers to discharge the ink to a recording medium from a plurality of nozzles communicated with the respective ink chambers. Another object is to provide an inkjet recording apparatus in which printing irregularities are reduced during printing.